1. Field of the Invention
The present invention relates to chip antennas, antenna devices, and mobile communication apparatus and more particularly to chip antennas, which are compact, flat-shaped antennas that may be used favorably in mobile communication apparatus, such as portable telephones, GPS (Global Positioning System) receivers, etc., and antenna devices and mobile communication apparatus.
2. Description of the Related Art
In recent years, compact size and light weight have come to be increasingly demanded of portable telephones, GPS receivers, and other mobile communication apparatus, and compact size is thus being demanded of parts used in such equipment. Since the antenna is a relatively large part among such component parts, compact size is being demanded of antennas in particular.
Given such circumstances, flat antennas, represented by microstrip antennas and one-side shorted microstrip antennas, have come to be developed as small antennas in accompaniment with the advancement of mobile communication apparatus. Among such antennas, the inverted F antenna 80, shown in FIG. 16, uses a dielectric ceramic substrate and is known as an antenna with which significant compactness can be achieved. The inverted F antenna 80 is provided with a substrate 81, made of a dielectric ceramic having magnesium oxide, calcium oxide, and titanium oxide as the main components thereof and with a relative dielectric constant of 20. Here, inverted F antenna 80 has a shape for example of 13.0 mm length.times.13.0 mm width.times.6.0 mm height. Metal conducting films of copper are deposited onto the upper and lower surfaces of substrate 81 respectively to form a radiating conductor 82 and a grounding conductor 83. A shorting conductor 84, which is of predetermined width and is made of a metal conducting film of copper that shorts radiating conductor 82 and grounding conductor 83, is formed by deposition on the side surface of ceramic substrate 81. Also in order to feed to this inverted F antenna 80, a feed conductor 85 is provided so as to extend from a prescribed position of radiating conductor 82 and along the side face of substrate 81. In using such an inverted F antenna 80, the grounding conductor 83 at the lower surface of substrate 81 is set to contact for example the metal chassis of a portable telephone so as to use the antenna as a receiving-only antenna. In this case, inverted F antenna 80 operates as a microstrip type inverted F antenna. With such an inverted F antenna, the following relationship holds for the resonance frequency f; EQU f=1/(2.pi..multidot.(LC).sup.1/2)
where L is the inductance component of the radiating conductor and C is the capacitance component between the radiating conductor and the grounding conductor, and for example, the resonance frequency in the case of inverted F antenna 80 (FIG. 16) will be approximately 800 MHz.
However, with the conventional inverted F antenna described above, when the resonance frequency is to be made lower to enable use down to the low frequency range, the capacitance component between the radiating conductor and the grounding conductor has to be made large, and for this, the interval between the radiating conductor and the grounding conductor had to be made extremely narrow, thus presenting the problem of requiring precision in manufacture.
Also due to restrictions in the precision of manufacture of the interval between the radiating conductor and the grounding conductor, a limit was placed on the capacitance component between the radiating conductor and the grounding conductor, thus giving rise to the problem of the range of variation of the resonance frequency being narrow.